1. Field of the Invention
The present invention relates to novel cyclic onium compounds; more specifically, it relates to cyclic sulfonium compounds and cyclic ammonium compounds useful as a glucosidase inhibitor for inhibiting the glycolytic activity of glucosidase, and a glucosidase inhibitor using these compounds.
2. Description of Related Art
Use of a glucosidase inhibitor that inhibits glycolytic activity of the glycolytic enzyme glucosidase can suppress absorption and digestion of sugar in the intestines, etc. Thus there are hopes for the usefulness of glucosidase inhibitors as a drug for treatment or prevention of diabetes. Known examples of compounds used as such a glucosidase inhibitor include cyclic sulfonium compounds such as a thiacyclopentane derivative and thiacyclohexane derivative where the sulfur atoms have a valence of 3.
For example, claim 8 of JP 2002-179673 (patent document 1) discloses as a compound having glucosidase-inhibiting activity a cyclic sulfonium compound represented by the following structural formula (III):

Meanwhile, Tetrahedron Letters, Vol. 38, No. 48. pp. 8367-8370 (1997) (non-patent document 1) discloses that salacinol, which is an essential pharmacological substance contained in the medicinal plant salacia reticulata used in traditional medicine in India, is a powerful glucosidase inhibitor, and the structural formula of salacinol is further disclosed. The cyclic sulfonium compound of formula (III) has a structure similar to that of the salacinol and demonstrates similar glucosidase-inhibiting activity.
Further, JP 2002-51735 (patent document 2), for example, discloses an antidiabetic food containing salacinol.
It is an object of the present invention to provide a cyclic sulfonium compound and cyclic ammonium compound having glucosidase-inhibiting activity equivalent or superior to those of known glucosidase inhibitors such as salacinol.
The inventors of the present invention discovered, following careful examination of a variety of cyclic sulfonium compounds and cyclic ammonium compounds, that novel cyclic sulfonium compounds that are thiacyclopentane derivatives or thiacyclohexane derivatives with a specific structure and cyclic ammonium compounds with a specific structure have superior glucosidase-inhibiting activity, and thus made the present invention.    [Patent document 1] JP 2002-179673 A (claim 8)    [Patent document 2] JP 2002-51735 A (paragraph no. 8)    [Non-patent document] Tetrahedron Letters, Vol. 38, No. 48. pp. 8367-8370 (1997)